The present invention relates to control systems m general, and to voltage regulators in particular. Voltage regulators, such as DC-to-DC converters, are used to provide stable voltage sources for electronic Systems. Efficient DC-to-DC converters are particularly needed for battery management in low power devices, such as laptop computers and mobile phones. Switching voltage regulators (or simply xe2x80x9cswitching regulatorsxe2x80x9d) are known to be an efficient type of DC-to-DC converter. A switching regulator generates an output voltage by converting an input DC voltage into a high frequency voltage, and filtering the high frequency voltage to generate the output DC voltage.
Conventional switching regulators include two switches. One switch is used to alternately couple and decouple an unregulated input DC voltage source, such as a battery, to a load, such as an integrated circuit The other switch is used to alternately couple and decouple the load to ground An output filter, typically including an inductor and an output capacitor, is coupled between the switches and the load to filter the output of the switches and produce the output DC voltage.
The switches within the switching regulator are opened and closed according to commands from a closed-loop control system. Control systems within DC-to-DC converters, just like control systems generally within any electronic system, need to be stabilized. Care in the design of the control system in a DC-to-DC converter must account for variations of parameters such as the input voltage, filter inductor and capacitor values, switch resistances, printed circuit board parasitics, etc. Sometimes a simple scheme such as voltage feedback alone will stably control a power supply. In other situations, extra margin of stability and higher bandwidth are gained by using current mode control techniques. Still other schemes use hysteresis bands to decide how to control the switches.
In some cases, it is desired to add compensation to improve phase margin of a DC-to-DC regulator. Often phase margin can be improved by using a lag compensator, which lowers the overall bandwidth to boost phase at the crossover frequency. Unfortunately, with lowered bandwidth, DC-to-DC regulators take longer to respond to load current transients, resulting in larger output voltage deviations. As a result, many such systems use extra capacitance in the converter""s output filter to improve transient response. However, using larger capacitors increases the cost of the regulator substantially.
Commercially-available hysteretic controllers trigger certain responses when the output voltage deviates too high, or too low. However, these controllers do not have a beneficial effect on nominal, steady-state performance while the voltage is within the hysteresis bands, and may add design difficulty due to their non-linear behavior.
In one aspect, the invention is directed to a controller for use in a control system The controller includes a first gain element configured to provide a first predetermined gain to an output error signal describing an error in the output of the control system; a compensator including a control loop including a storage element, the control loop receiving the output error signal, a second gain element configured to provide a second predetermined gain to the output of the control loop, and a detector configured to modify the contents of the storage element according to a predetermined adjustment value when a minimum predetermined excursion occurs in the output error signal; and a combiner configured to combine the outputs of the first and second gain elements to produce an output control signal for the control system.
Implementations of the invention may include one or more of the following. The output of the control loop is the output of the storage element, and the control loop includes a third gain element configured to provide a third predetermined gain to the output error signal; a delay element configured to provide a predetermined delay to the output of the control loop; a fourth gain element configured to provide a fourth predetermined gain to the output of the delay element; and a second combiner configured to provide to the storage element the sum of the outputs of the third and fourth gain elements. The sum of the third and fourth predetermined gains is one. The detector is configured to load the storage element with the predetermined adjustment value when the minimum predetermined excursion occurs in the output error signal. The controller includes a combiner configured to load the storage element with the sum of the output of the control loop and the predetermined adjustment value when the minimum predetermined excursion occurs in the output error signal. The detector includes two or more comparison elements, each having a different range, and each associated with a different predetermined preload value, each comparison element configured to supply the predetermined preload value associated with that comparison element as the predetermined adjustment value when the output error signal is within the range of that comparison element The storage element can include an accumulator or an integrating capacitor. The detector can include an A/D converter.
In one aspect, the invention is directed to a controller for use in a DC-to-DC converter. The controller includes a first gain element configured to provide a first predetermined gain to an output error signal describing an error in the output of the DC-to-DC converter; a compensator including a control loop including a storage element, the control loop receiving the output error signal, a second gain element configured to provide a second predetermined gain to the output of the control loop, and a detector configured to modify the contents of the storage element according to a predetermined adjustment value when a minimum predetermined excursion occurs in the output error signal; and a combiner configured to combine the outputs of the first and second gain elements to produce an output control signal for the DC-to-DC converter.
In one aspect, the invention is directed to a DC-to-DC converter. The DC-to-DC converter includes a controller including a first gain element configured to provide a first predetermined gain to an output error signal describing an error in the output of the DC-to-DC converter; a compensator including a control loop including a storage element, the control loop receiving the output error signal, a second gain element configured to provide a second predetermined gain to the output of the control loop, and a detector configured to modify the contents of the storage element according to a predetermined adjustment value when a minimum predetermined excursion occurs in the output error signal; and a combiner configured to combine the outputs of the first and second gain elements to produce an output control signal for the DC-to-DC converter.
In one sect, the invention is directed to an apparatus for use in a control system controller having a control loop that includes a storage element, the control loop receiving an output error signal describing an error in the output of the control system. It includes means for modifying the contents of the storage element according to a predetermined adjustment value when a minimum predetermined excursion occurs in the output error signal; means for providing a first predetermined gain to the output error signal; means for providing a second predetermined gain to the output of the control loop; and means for combining the outputs of the first and second gain elements to produce an output control signal.
Advantages that can be seen in implementations of the invention include one or more of the following. The compensator can add phase margin without requiring extra capacitance, can provide enhance stability during steady-state conditions, and does not degrade transient response.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will become apparent from the description, the drawings, and the claims.